Here, we report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX 3 (MA = CH 3NH 3+, X = Br – or I –) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites’ precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaquemore » black with compression. Indeed, electronic conductivity measurements of (MA)PbI 3 obtained within a diamond-anvil cell show that the material’s resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br xI 1–x) 3 (0.2 < x < 1) reversibly form light-induced trap states, which pin their PL to a low energy. This may explain the low voltages obtained from solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors.« less

Here, we report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX 3 (MA = CH 3NH 3+, X = Br – or I –) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites’ precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaquemore » black with compression. Indeed, electronic conductivity measurements of (MA)PbI 3 obtained within a diamond-anvil cell show that the material’s resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br xI 1–x) 3 (0.2 < x < 1) reversibly form light-induced trap states, which pin their PL to a low energy. This may explain the low voltages obtained from solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors.« less

A simple “cast-capping” method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH{sub 3}NH{sub 3}PbBr{sub 3}). By capping a CH{sub 3}NH{sub 3}PbBr{sub 3} solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry–Pérot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of μm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained frommore » a planar crystal grown between two DBRs with a cavity thickness of a few μm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal.« less

A comprehensive view of the microstructure of (111)B CdTe films grown on miscut (001)Si substrates by molecular beam epitaxy has been obtained by transmission electron microscopy and scanning transmission electron microscopy. It is found that in the initial growth stage, CdTe nucleates with a dominance of one particular domain: a domain with (111)B polarity and orientation of [11{minus}2]CdTe//[1{minus}10]Si, although there are also some other domains of different polarity and orientation. The dominance of one type domain is due to the reduction of the surface symmetry by using the miscut substrate and by using optimum growth conditions. As the growth proceeds,more » a single-crystal film is produced by the dominating domain overgrowing the minority domains nucleated at the film{endash}substrate interface. This results in the final film of single-crystal character having (111)B polarity with [11{minus}2]CdTe along [1{minus}10]Si. {copyright} {ital 1998 American Institute of Physics.}« less

We report the growth of single-domain epitaxial Bi{sub 2}Se{sub 3} films on InP(111)A substrate by molecular-beam epitaxy. Nucleation of Bi{sub 2}Se{sub 3} proceeds at steps, so the lattices of the substrate play the guiding role for a unidirectional crystalline film in the step-flow growth mode. There exists a strong chemical interaction between atoms at the heterointerface, so the growth does not follow the van der Waals epitaxy process. A mounded morphology of thick Bi{sub 2}Se{sub 3} epilayers suggests a growth kinetics dictated by the Ehrlich-Schwoebel barrier. The Schubnikov de Haas oscillations observed in magnetoresistance measurements are attributed to Landau quantizationmore » of the bulk states of electrons.« less